The Neutralizing Antibody Scientific Research Support Component will provide essential laboratory and scientific support for CHAVI- by performing high throughput assessments of neutralizing activity against tier 1 and tier 2 reference HlV-1 strains in standardized and validated assays. In addition, we will map the epitopes of broadly neutralizing sera and mAbs, monitor vaccine-elicited nAb responses to identify improved immunogens, adjuvants and vectors, and delineate nAbs as a correlate of protection using breakthrough viruses from phase 2b trials. Specific Aims Aim 1. To support CHAVI-ID research by defining the magnitude and breadth (M-B) of neutralizing activity in sera from select clinical groups, and by mapping the epitopes of broadly neutralizing sera. Aim 2. To support CHAVI-ID research by screening memory B cell culture supernatants to identify nAb-producing B cells. Aim 3. To support CHAVI-ID research by characterizing new mAbs for magnitude and breadth of neutralizing activity and epitope specificity. Aim 4. To support CHAVI-ID research by monitoring the magnitude and breadth of vaccine-elicited nAbs in animals, human vaccinees, and by assessing vaccine sera neutralization with viruses from vaccine breakthrough infections in humans.